This invention relates to a sizing agent for the treatment of glass fibers for plastics and to a method for the treatment of glass fibers by the use of the aforementioned sizing agent. More particularly, this invention relates to a sizing agent for the treatment of glass fibers excelling in ability to bundle glass fibers and in affinity for matrix resin and to a method for the treatment of glass fibers by the use of said sizing agent.
When glass fibers are used for reinforcing plastics, specifically when they are used as reinforcing material for shaped articles of thermosetting resins represented by unsaturated polyester resin or shaped articles of thermoplastic resins, typically by polystyrene, the glass fibers are treated in advance with a sizing agent which is composed of coupling agent, film-forming agent, lubricating agent, etc.
This invention relates to a sizing agent for the treatment of glass fibers, characterized by containing the film-forming agent as described in detail below.
A film-forming agent is an indispensable component for protecting the surface of glass fibers against damage by friction during the manufacturing process of glass fiber products and also for heightening the ability of a sizing agent to bundle glass fibers. When glass fibers are used for the reinforcement of plastics, i.e. in the manufacture of reinforced plastic materials, the film-forming agent forms the primary cause for retarding the impregnation of the matrix resin into the glass fibers.
At present, the polymer and copolymer of vinyl acetate and peracrylic esters are most widely used as film-forming agents. These film-forming agents amply serve to heighten the ability to bundle glass fibers but on the other hand, degrade the affinity of the matrix resin to the glass fibers.
With a view to permitting manufacture of reinforced plastics of high strength able to provide the incompatible properties of ability to bundle glass fibers and affinity between glass fibers and matrix resin, various studies have been made on formulations of sizing agents. For example, Japanese Patent Publication No. SHO 48(1973)-28997 discloses a sizing agent which uses a mixed emulsion of polyvinyl acetate and polystyrene as film-forming agents and consequently imparts glass fibers excellent permeability to the matrix resin. In this case, however since the polymers are by nature deficient in compatibility, they are liable to induce phase separation and consequently fail to produce reinforced plastic materials of high strength. Japanese Patent Application Disclosure No. SHO 53(1978)-17720 discloses that reinforced plastic materials of great strength can be obtained by using a sizing agent containing organic peroxides of high thermal stability. Further Japanese Patent Application Disclosure No. SHO 56(1981)-140048 discloses a method for enhancing the affinity between glass fibers and matrix resin by using organic peroxides in the form of an aqueous emulsion. It has been demonstrated that in these methods highly reactive organic peroxides are liable to inflict damage to the surface of glass fibers, and rigidify and embrittle the coatings because they are locally concentrated on the surface of the glass fibers. This adverse effect arises because a large quantity of organic peroxides are required in consequence of low catalytic efficiency. The aforementioned defect of the sizing agent is not eliminated by the conversion of the organic peroxide into the aqueous emulsion.
The conventional sizing agents have had much room for further improvement as described above.
An object of this invention is to provide a sizing agent for the treatment of glass fibers which has enhanced ability to bundle glass fibers and imparts to the glass fibers ample affinity for the matrix resin.
Another object of this invention is to provide a method for the treatment of glass fibers by the use of the aforementioned sizing agent for the treatment of glass fibers.